swift学习--控制流
判断 if判断 普通条件判断 func demo2(){ let url = NSURL(string: "www.baidu.com") //if判断url 可选类型有没有值 if url != nil {
let request = NSURLRequest(URL: url!) print(request) } } //if let 判断可选类型 有值才执行 没值就不执行 func demo3(){ let url = NSURL(string: "www.baidu.com") if let u = url{ let request = NSURLRequest(URL: u) print(request) } } //if let 多个可选类型判断 func demo4(){ let name: String? = "张三" let age: Int? = 20 if let n = name,a = age{ print("(n)(a)") } } //guard let 判断可选类型常量变量有没有值 有则赋值给定义的常量或者变量 如果没有则执行else语句 func demo5(){
let url = NSURL(string:"www.baidu.com") //guard let判断 guard let u = url else{ print("url 为nil") return } let request = NSURLRequest(URL: u) print(request) } //if let 后边跟where语句 func demo6(){
let url = NSURL(string: "http://www.baidu.com")
//if let 判断url 存在 where条件 域名是不是百度 if let u = url where u.host == "www.baidu.com"{ //再次判断 u.host的可选类型 if let s = u.host{ let request = NSURLRequest(URL: u) print(request) print(s) } } } //if let 多个参数 where语句判断 func demo7(){
let name:String? = "张三" let age:Int? = 20 if let a = name,u = age where a == "张三" && u == 20{ print(a,u)
} } // switch 判断 /* swift 可以判断任意类型 可以省略break 是可以省略大括号'{}' case 后面一定要有执行语句 func demo9(){
let score:Int? = 93
guard let num = score else{ print("nil") return } switch num{ case let x where x > 90: print("sf") default: print("s") } }
//switch func demo8(){
let scoreStr:String? = "良" guard let u = scoreStr else{ print("nil") return } switch u{ case "优": print(u) case "良": print(u) default: print("差劲") } } (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |